Crystal structure of calcium zirconium diorthophosphate, CaZr(PO₄)₂

Abstract

The crystal structure of CaZr(PO 4 ) 2 was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was orthorhombic (space group P 2 1 2 1 2 1 , Z =4) with a =1.448 76(4), b =0.672 13(1), c =0.623 47(2) nm, and V =0.607 10(3) nm 3 . Final reliability indices were R wp =6.49%, R B =2.43%, and S =1.32. The Ca atom is sevenfold coordinated, and the Ca atom and surrounding oxygen atoms form a distorted capped octahedron with a mean Ca–O distance of 0.243 nm. The ZrO 7 coordination polyhedron is a distorted pentagonal bipyramid with a mean Zr–O distance of 0.216 nm. CaO 7 , ZrO 7 , and PO 4 polyhedra share edges to form infinite chains with the composition [CaO 3 ZrO 3 P 2 O 8 ] 12− along the [010]. Individual chains are linked together, forming a two-dimensional sheet parallel to (100). These sheets are stacked in the [100] direction to form a three-dimensional structure.